1. Field of the Invention
The present invention relates to a metal-polishing method, and particularly to a method of removing micro-scratches on a metal layer.
2. Description of the Prior Art
In semiconductor technology, metal layers are applied to wire various components formed on a semiconductor wafer. The metal wiring process includes patterning and etching a hole within a thick layer of dielectric layer. Thereafter, a conformal barrier layer, such as Ti, TiW or TiN layer, is provided on the dielectric layer and within the hole. The conformal barrier layer functions to separate the dielectric layer from a metal layer deposited subsequently. After barrier layer deposition, a metal layer is deposited to over-fill the hole. The hole created prior to the metal deposition defines a metal pattern, so that a desired wire line will be formed after a planarizing technique removes the metal layer outside the hole.
Chemical mechanical polishing (CMP), an example of the above planarizing technique, uses apparatus similar to a grinder wheel along with a reagent to mechanically grind off the uneven profile of a semiconductor wafer. When the CMP is applied to form metal lines by the metal wiring process described above, it is referred to as a damascene process.
The reagent is usually referred to as xe2x80x9cslurryxe2x80x9d. Slurry is a solution mixed with chemicals and abrasive particles. The abrasive particles are extremely hard and have a diameter of about 0.1-0.5 micrometers.
During polishing by a CMP apparatus, the abrasive particles with large size are filtered by a filter in order to reduce the micro-scratches on the metal surface. However, particles with small size are easily agglomerated into a large size particle. Moreover, while the polishing process stops, even the large size particles deposit. Those large size particles scrape the metal surface and leave micro-scratches thereon, thereby decreasing the yield of the damascene process. Accordingly, we need a method of removing the micro-scratches on a metal surface.
It is an object of this invention to provide a method of removing the micro-scratches on a metal surface.
Other objects and advantages of this invention will become apparent to those of ordinary skill in the art having reference to the following specification in conjunction the drawings.
The invention may be incorporated into a method of removing the micro-scratches on a metal layer, wherein the metal layer is formed on a barrier layer conforming onto a dielectric layer having a hole thereon, and wherein the metal layer over-fills the hole. The metal layer is chemical-mechanically polished, to oxidize and polish away the metal layer outside the hole, with a first slurry, wherein the slurry has a chemical solution and has a plurality of abrasive particles. The barrier layer is chemical-mechanically polished to oxidize and polish away the barrier layer outside the hole with a second slurry, whereby micro-scratches are formed on the metal layer. The metal layer is chemical-mechanically polished again, to buff the metal layer, with the first slurry, thereby removing the micro-scratches on the metal layer.
The metal layer is preferably buffed for about 1 to about 30 seconds with the slurry. Moreover, the buffing slurry has a preferable chemical concentration less than that of the slurry used for oxidizing and polishing away the metal layer outside the hole. The chemical concentration is lowered for slowing down the buffing removal rate. However, alternatively, the buffing removal rate can also be slowed down by reducing the number of the abrasive particles from the slurry. Another method of slowing down the polishing removal rate is to adjust the parameters of the CMP apparatus.